RV8 FI Pressure

[Transmitter Man]

I believe the RV8 requires 3 Bar of pressure.

What is that in old money (LBS)?

I'm looking at fitting an 'electric' fuel pressure gauge in the dash. I can find 0-15 and 0-100 PSI gauges.

(All fuel stays in the engine bay)

http://www.autometer.com/cat_gaugedetail.aspx?gid=...

http://www.autometer.com/cat_gaugedetail.aspx?gid=...

Thanks.

Phil
420 SEAC

[carob]

Hi Phil,

3 bar = 43.5 psi

Rob

[plushuit]

Transmitter Man said:

I believe the RV8 requires 3 Bar of pressure.

What is that in old money (LBS)?
I'm looking at fitting an 'electric' fuel pressure gauge in the dash. I can find 0-15 and 0-100 PSI gauges.
(All fuel stays in the engine bay)
http://www.autometer.com/cat_gaugedetail.aspx?gid=...
http://www.autometer.com/cat_gaugedetail.aspx?gid=...
Thanks.
Phil
420 SEAC

3 bar is 43 psi. The Rover V8s run at 36-38 psi..unless you have intervened for some reason. The pressure will also vary with heat, vacuum etc etc.. but 36-38 is what one sets it at with a stock Flapper or all Hotwires.

Fuel pressure gauges are a great tool..especially for Flappers. A glance and you know whether your non-working car has a fueling or ignition problem (can only be one of the two). But for that reason, they are best installed in the engine bay..on an adjustable fuel pressure regulator. I combined a US-purchased gauge with an FSE and it is great. The combination has been copied by a couple of suppliers. The gauge (with a 90 degree adapter) threads into the unused threaded hole on the FSE side.

If you want a much wider choice of gauges..consult Jegs or Summit Racing. I use a 0-60psi.
http://tinyurl.com/6ey3c23 or http://tinyurl.com/3ccgw9y

L.

Edited by plushuit on Saturday 6th August 18:07

[pjtvr390se]

It should tick over in the region of 26psi, that is why the pressure regulator has a vacuum connection to the plenum which pulls down the pressure ,if it ticks over at 35psi it will be over fueling. My old pressure regulator had failed on the vacuum side and failed the emission test at MOT time badly but it ran fine at anything above idle. If you have a gauge fitted and blip the throttle at idle, the pressure will shoot up to the 35psi or whatever it is set at from your set idle pressure. I learnt the hard way about this as I couldn't figure it out, £15 gauge and it was obvious. I fitted my gauge to pipe that feeds the cold start injector, the easiest place for quick connection. Don't forget to de-presurise the fuel system before disconnecting any fuel pipes, the method is in all fuel injection manuals that I have seen so I won't bore you with it here.

[plushuit]

pjtvr390se said:

It should tick over in the region of 26psi, that is why the pressure regulator has a vacuum connection to the plenum which pulls down the pressure ,if it ticks over at 35psi it will be over fueling.

The reason the regulator is called a "rising rate" is because it allows fuel pressure to rise in demand scenarios. Floor the accelerator, and you will see pressure jump far higher than 35 psi. You should not be running as low as 26psi..with one codicil. One the weaknesses of the Flapper systems is that it has no mechanism to handle the issues of hot fuel. Indeed, when you stop a hot engine, it will struggle to start again as the fuel in the rail is gaseous and insufficiently dense to start the car smoothly. After it circulates a bit..all is well until the next time.

Of course, the later 14CUX system added a fuel temperature sensor that allows the computer to adjust the amount of injected fuel to compensate. Here is something little known these days. The Australian Rover division designed a subsystem to help Flappers with the hot start problems..way back in the 1980s. They installed a temperature controlled solenoid in the fuel lines that would block the line and send the fuel pressure up, resolving the issue. Ingenious.

I have to disagree with you on 26 psi. On a flapper, that would reflect a faulty test, a faulty fuel pressure regulator or simply hot fuel. You can confirm this with a quick google. If you would like, I can post the relevant pages from the LR Factory manual.

Test the pressure when the engine is cold. Turn on the ignition without engaging the started. Remove air filter-to-AFM conduit and move the AFM flap to make the pump work. Then see what psi you have.







From the Land Rover's Dealer Workshop Manuals;

Flapper - Bosch L-Jetronics

[pjtvr390se]

plushuit said:

Test the pressure when the engine is cold. Turn on the ignition without engaging the started. Remove air filter-to-AFM conduit and move the AFM flap to make the pump work. Then see what psi you have.

I agree, when I do that the fuel pressure instantly goes up to 35psi and gradually, after the engine starts and warms up drops to 26psi at hot tick over. Starts fine hot as the fuel pressure is 35psi as there is no plenum vacuum, when the engine is not running, to lower the pressure supplied by the fuel pressure regulator.

[E Ponym]

The FI system in the Rover V8 measures the fuel delivery by time, i.e. the time the injectors are open.

This assumes that the pressure difference between the fuel line and the nose of the injector - that is why the plenum vacuum is important to fuel pressure. If the fuel demands of your engine show that your injectors are open all the time at high revs/power then you either need to put bigger injectors on or increase the fuel pressure (this only works over a limited range).

So pjt's ficure of 26psi is relative to a high plenum vacuum at idle, if the fuel pressure is measured with the engine stopped but the fuel pump running (flap open) then I would expect to see a higher pressure. It is probably better to set up with the engine stopped because idle vacuum can vary so much with little things (extra air valve open, sticky idle over-run valve, sticky throttle etc.).

Russ

[Transmitter Man]

I started this thread and am learning a great deal about fuel regulators and expected pressure readings. I had always wondered why some people suffer with difficult hot starting and had always thought that there was something not quite right on the fuelling side.

Lorne,

Jeg's do not ship Internationally although I have a drop ship address in California for any US imports. I have dealt with Summit Racing for some years.

During my car's rebuild I would prefer to monitor fuel pressure inside the cockpit together with air/fuel ratio. Auto Meter's electric fuel pressure gauges come with sender units that keep the fuel in the engine bay!

I will be installing a Megasquirt 2 ECU to control things.

I just fancy trying to optimise the operation of my Rover V8.

Trying to connector Taylor Racing 10.8mm diameter ignition leads into Ford coil packs is my latest hurdle.

Thank you all for your comments and suggestions. So the 0-100 psi gauge it is then.

Phil
420 SEAC

[plushuit]

Transmitter Man said:

Lorne,

Jeg's do not ship Internationally although I have a drop ship address in California for any US imports. I have dealt with Summit Racing for some years.

Both good companies. Candy stores for car nuts. They CAN get weird when sending stuff outside the USA but they are hard to resist nonetheless. Many UK companies will not ship the USA. Their insurance companies will not cover their liability for parts shipped there.

I pack a significant part of baggage taking parts from Canada to the UK and from the UK to Canada. Mid-Atlantic motors.

Transmitter Man said:

During my car's rebuild I would prefer to monitor fuel pressure inside the cockpit together with air/fuel ratio. Auto Meter's electric fuel pressure gauges come with sender units that keep the fuel in the engine bay!

Sounds good. At the price, why not mount an extra one in the bay. You will thank for it. Go for the 0-60.

Transmitter Man said:

I will be installing a Megasquirt 2 ECU to control things.

I would be fascinated to hear everything about that. Step by step if you have the time..with images:.I have read good things about Megasquirt. It sounds like a smart direction for some.

Transmitter Man said:

I just fancy trying to optimise the operation of my Rover V8.Phil

Don't we all!

Lorne

[plushuit]

E Ponym said:

The FI system in the Rover V8 measures the fuel delivery by time, i.e. the time the injectors are open.

This assumes that the pressure difference between the fuel line and the nose of the injector - that is why the plenum vacuum is important to fuel pressure.

The ECU simply governs the fueling by varying the duration the injectors are open. However, a flapper has no fueling feedback after the fact for its ECU (aside from the rare ones with Bosch L-Jetronic [ugh] closed-loop lambda control). And the fuel map is linear. So you can increase fueling by simply increasing the fuel pressure. The injectors are open for the same duration but, with the added pressure, more fuel is delivered in the same intervals.

E Ponym said:

If the fuel demands of your engine show that your injectors are open all the time at high revs/power then you either need to put bigger injectors on or increase the fuel pressure (this only works over a limited range).

The injectors can only be on all the time if there is something amiss..i.e., some or all of the wires to the injectors are earthed. (it usually will occur by injector bank..4 on one side and the 4 on the other). That will stop the engine and even hydro-lock it.

I use both options you note to fuel the two engines I have in the cars at the moment. For the high compression 4.8, I use Jag injectors. Keeps the fuel pressure down to only a little higher than 3.5 stock. For the other car in the UK...interesting story with that.

I had spent 5 weeks driving in France adding a liter or two coolant everyday because of sad head gaskets..a common pre-composite gasket problem. Got back to the UK, drove up to Rpi and bought a new 4.6. (This was obviously pre-2009) But the deal was that I would borrow a bay, a lift and a second pair of hands and do the swap on the spot. We started at 10AM and I was test driving the thing at 9AM the next morning. Their EFI tuning fellow adjusted the fuel pressure and AFM with a exhaust gas analyzer. Idled great but he left the fuel pressure at 36 psi.

I am a believer in very limited break-in for these engines when they are placed in a sports car. Sports cars are too light and do not provide sufficient load to bed in the rings and cylinders as they would if pushing a 3 ton 4x4. Most often, the "safe" procedure only glassifies the cylinder walls. But I was kind to the car for 300 miles..never floored the accelerator, never went beyond 3000 rpm. So, by the time I ran into a problem, we were many miles away.

The problem was that the car would NOT rev over 3500. I thought about that as I puttered along trying to hide my concern from SWMBO I came to the conclusion that there is no way a flapper ECU can figure out needed air-fuel mixture results. In this case, it was trying to feed a 4.6 with a 3.5's fueling. So I calculated as follows; 4.6/3.5 x 36psi = 47-48 psi. At the next stop, I increased the pressure (I use FSE regulators with gauges) to 48 psi and lowered the resultant idle. That is pretty much it. Car immediately sailed past 5500 and topped out at 6200. I bought a little Gunson Co2 analyzer at the next Halfords and trimmed the AFM to spec at leisure.

I had the opportunity to speak to Mark Adams a week or so later. He heartily approved. The downside of increasing pressure is that you are putting the hoses and connections under a bit more stress. But many EFIs run at much higher than 50psi. The good side is that higher pressure produces a finer, more combustible spray from the injectors and that shows up in a smoother idle and acceleration. Of course, you can only do this with an analogue ECU AFAIK. A later digital system will simply fall into default mode and limp home.

E Ponym said:

So pjt's ficure of 26psi is relative to a high plenum vacuum at idle, if the fuel pressure is measured with the engine stopped but the fuel pump running (flap open) then I would expect to see a higher pressure. It is probably better to set up with the engine stopped because idle vacuum can vary so much with little things (extra air valve open, sticky idle over-run valve, sticky throttle etc.). Russ

Correct. A common point of reference is necessary. You can't get that as accurately if the car is running.

Lorne

Edited by plushuit on Sunday 7th August 15:45

[Wedg1e]

My car runs non-standard injectors and 1.8Bar at idle (otherwise it won't start!). It has the 390SE's standard variable (but non-rising-rate) pressure regulator and the AFR graph shows a pretty flat line across the board.
According to the histoy file the previous owner had an FSE regulator fitted to it but, like a few other things, they seem to have disappeared on the car's journey through the dealer I got it from

[carob]

One thing to consider is the accuracy of gauges. A brand new of the shelf guage normally comes with a 0.5 bar +/- accuracy i believe. so older ones have the chance to be more out. Just something to consider.

Rob